In the field of an electrophotographic image forming apparatus, it is common practice to employ a structural arrangement were one or more among developer, photosensitive member, processing means, etc., are assembled in the form of a cartridge so that they can be removably mountable in the main assembly of an electrophotographic image forming apparatus. A cartridge used with an image forming apparatus is driven by a driving apparatus with which the main assembly of the image forming apparatus is provided. More specifically, the cartridge is driven by the driving apparatus, through a driving force transmitting apparatus, that is, the connective means positioned between the cartridge and the main assembly of an image forming apparatus. The driving force transmitting apparatus is made up of gears, coupling members, etc.
In a case where an image forming apparatus is structured so that a cartridge therefor is to be mounted or dismounted in the direction parallel to the lengthwise direction of the cartridge, it is common practice that one of the lengthwise ends of the cartridge is provided with a coupling member, which functions as a part of the means for transmitting driving force to the cartridge from the main assembly of the image forming apparatus.
Regarding the coupling means structure, a coupling means is made up of two portions, that is, a portion with a protrusion (claw or the like) and a portion with a recess. The protrusion protrudes in parallel to the rotational axis of the coupling. The portion with a recess is rotationally driven by the portion with a protrusion by engaging with the protrusion. In the case of the coupling structured as described above, the coupling portion with a protrusion is attached to the cartridge, and the coupling portion with a recess is attached to the main assembly of the image forming apparatus.
The two coupling portions sometimes fail to couple with each other. That is, the projection sometimes fails to fit into the recess, because of the relationship in terms of rotational phase. More specifically, the two coupling portions interfere with each other in terms of their movement in the direction parallel to their axial lines, and therefore, they sometimes prevent the cartridge from being completely mounted into the main assembly of the image forming apparatus.
Thus, some of the conventional driving force transmitting apparatuses made up of a coupling means are structured so that the portion of the coupling means, which is attached to a cartridge, or the portion of the coupling means, which is attached to the main assembly of an image forming apparatus, is fitted with a spring which allows the corresponding portion of the coupling means to retract in the direction parallel to the axial line of the coupling means if the coupling means interferes with the mounting of the process cartridge into the main assembly of the image forming apparatus (Japanese Laid-open Patent Application 2005-107413). In the case of most of the conventional driving force transmitting apparatuses of the above described type, the portion of the coupling means, which belongs to the main assembly of an image forming apparatus, is provided with a spring which keeps this portion of the coupling means pressed toward a cartridge while allowing the coupling porting to retract in the axial direction of the coupling portion. Further, these driving force transmitting apparatuses are structured so that even if the protruding portion of the coupling means does not properly fit into the recess of the coupling means when a cartridge is mounted into the main assembly of an image forming apparatus, the portion of the coupling means, which belongs to the main assembly of an image forming apparatus, retracts in its axial direction. Therefore, the coupling portion of the cartridge and the coupling portion of the apparatus main assembly do not interfere with the inward movement of the cartridge into the apparatus main assembly in their axial directions, allowing thereby the cartridge to be completely mounted into the apparatus main assembly. The difference in rotational phase between the two coupling portions is eliminated by the rotation of the coupling portion of the apparatus main assembly. Thus, the coupling portion which had retracted is allowed to be moved by the resiliency of the abovementioned spring in the axial direction of the coupling portion (toward cartridge). As a result, the coupling portion with the protrusion, and the coupling portion with the recess, properly engage with each other, making it possible for the driving force to be transmitted.